While I don’t know the cause of the acf/load_value filter issue I would use the acf/prepare_field filter for making a change like this.
I see that the developer asked you for code, so I won’t make you post it twice. You should post your filter code over on github for them to look at. You could also post it here but I’ll probably defer to letting them look at it first.
https://github.com/AdvancedCustomFields/acf/issues/632
